Roasting of ores, especially zinc sulphide ores containing lead and/or cadmium



Oct. 4, 1938. 1 s. ROBSON ET AL 2,131,786

. ROASTING 0F ORES, ESPECIALLY ZINC SULPHIDE ORES CONTAINING LEAD AND/ORCADMIUM Filed May 15, 1957 2 Sheets-Sheet l 1 INVENTORS I STANLEY RoBsoNTHOMAS BENSON GYLES ATTORNEYS Oct. 4, 1938. v s. ROBSON ET AL 2,131,786

ROASTING OF ORES, ESPECIALLY ZINC SULPHIDE ORES CONTAINING LEAD AND/ORCADMIUM Filed May 15, 1957 2 Sheets-Sheet 2 INVENTORS STANLEY ROBSONTHOMAS BENSON Gvuas ww w ATTORN E YS Paten ted ett '4; 193 8 I I b I it2 m'f I I ROASTING or ones, ESPECIALLY. zinc SULPHIDE ORES CONTAININGLEAD AND/R. CADMIUM 1 I v Stanley Robson; Durdham Park, Bristol,Gloucester, and Thomas Benson Gyles,.Clitton',- Bristol, Gloucester,England, assignors to National Processes Limited, London, England, an 1Englishjoint-stockcompany I I Application; May 15,1937, Serial No.142,780

In Great Britain May 21, 1936 i v a m 101. 15-1) I p This inventionrelates to processes and means teririg machineigwhich can beeasily-separated- I or or relating to roasting ores particularly zincinto two layerssso that the upper layer or the sulphideores,'concentrates and the like (allherecake which is relatively free'from lead or cad-- I -inafter referred to as the ore) in which anysuitm y e separated V fromflnd d r d 1 b t; roaster l u a .b empldyed,-separately from the lower layer of the charge .5 for example blastroasting apparatusof the well in which the lead or/aud cadmium isconcen:

- known "DwlghtJ-loyd type'in which the ore to rai rmainly eonchtrated-I I .be sintered is delivered on to the surface of travel- I Accordingto the inven i n a pr cess for .ro'ast- I ling grates so as to formthereon-a bed or charge, lng zinc sulp ores, containing l an '10 ofsuch'ore of suitable thickness which travelling cadmium consists inarranging the one charge on .bed of ore or-charge is'caused, to passbeneath, thetravelling d ofa sinteringma in in 3 an ignition burner orburners and over a suction lay s a p t li -r y se a ated, byinterachamber or chambers whereby the ore is sintered' posing afley r 1 mterial which is either (a) inand thereafter delivered-oil the machine,for exert during the rcasting opera 1 n r lbf 11-. x m l as r be 1 mipatent spgciflcatlgn ferent grain size or (c) 01' dliferent sulphur.con-.- 16 v Nix-306.569; or if desired in carrying out the I tentof fuelvalue from t ma n/char e. where- I present invention any other suitablel'orm of by when the chargeis sintered' a plane of cleav I blast roasterapparatus may be employedin which age in the charge lsj fo med btweenthe upper 1 cment a of 8417 or oxydizmg' atmosphere is and lowerlayers of the-ore charge. I r 4 20 blown-or drawn through a charg'e'forbed of ore The lollowing a eexamples three e a i 2,

on a perforated travelling grate, I, I i methods 0! pr due n ythe pl nof c ava in According to this invention the bed-orcharge e s nt r d akeW cha e mp ll of ore to be sintered is composedol 3 layers or I a an inr layer y b 'l e p d be we n 1.: dill g materials in thecontiguouslayerswhich the top and bottom a s y spreading over the g areeach prepared and laid, superimposed, on one om por i n ttom layer). ofthe char a another, on the travelling grate so that when the I zinc orecontaining nq l h r such for example .7 3

complete bed orore'or charge thus formed on as'calamiue or alreadydesulphurizedzinc'ore-or the trave l lfi grate has been subjected to theS a er- In this case the interp a er wil 7 ,sinterlng operation thethu's sintere'd bed of ore main inert during the roasting pro ess,whereas to or charge will produce 'or provide aplane or easy t e lay rae n l yer below it being the mm I or ready cleavage whereby this.sintered-t'ravel Inal charge in ng. 1 1' example! en r ling bed orcharge of ore ca'n bereadily separated I and returned sinter willformtwo slnter layers into two layers advantageously when about to s aratedby the interposed in t and h s al' r. leave or as same leave thetravelling grate. thus Iorming a planeof cleavage.

a 1 This invention refers particularly to-the blast 1 (b) All'ayer ofdiflering' grain size'may be in roasting or zlnc'sulphide ores (blende'contain. .terbosed by dus n ve y fine slntered returns I ing impurities,notably lead and/or cadmium; 1 on to the bottom layer before eed n n tos n communds :or other ,compoundswhich may bethe top layer material; orby using for the infipresent and which readily volatilize whenttigetermediate'layer the same mixed charge mate- 40 said o'res are heatedi'n processes. of the type in 1181 as the t pand o m ayers, vbut havin40 which the roastedproduct is obtained .in a- 5111: "for theintermediate layerra particle size'coarser- Y tered jiorm and we. willproceedto describe our than the rest'oi the charge. In thislatter-case,- I presentinyention:withr r r t tm kmd (if 2 although theshrinkage maybe of-or about-the ore., V I same order asgthe upper andlower: layers, yet It has been observed-in practice thatthelead thedlil'erencein particle -size will cause 'thej or/andcadmiu'm presentin-thesintered charge coarser material or the' intermediate layer to a 4j from a 'zinc 'sulphideore (blendel chargedonto form a loose rubblylayer whicheasilyparts be- -.a 'sintering Zmachine is notevenly,,distributed tween the upper and. lower layers. I I vtherethrough-on completion oith'e vsinteringj (ciAn interposed layer ol'diilerent sulphur I operation-i. e.-the bottom-portlons-oithe sinter[content orluelvalue can be produced by mak so 1 cakenowhaving amuchgreater proportion. or in: a lflerent mixture of green ore than thev theselelements than the t p portions which latter main charge so as toproduce a mixture for-the are relativelyzfre hereof. intermediate layerha n eithera high r or w- It is an object 01' this invention to pro'duce:a er sulphur contentthan that of the main charge.- aintered cake (onthe travelling state, or the sinf In this case, the dilrerent'roastingintensity will cause a different shrinkage between the interposed layerand the layers above and below thus forming a plane of cleavage. Thesame efiect will also be obtained by forming the interposed layer ofdesulphurized sinter with which sufficient fuel is admixed which burningin the air current will produce a difierent temperature in theinterposed layer and consequently form a cleavage plane. I

The process of the invention may be employed in any well-known sinteringprocesses to which same may be applicable as, for example, in thewell-known two-stage process (patent specification No. 1,401,733) inwhich the material is sintered (after previous roasting in apre-roasting furnace) using green ore as the additional fuel. Theinvention may also be applied to similar processes as, for example,where coal or coke or carbon is used as the fuel in the sintering ofmaterials previously desuiphurized.

The invention is, however, particularly applicable in carrying out theprocess set out in British patent specification No. 306,569 and incarrying out the process set out in British patent specification No.433,861. In these processes the invention may be employed in any of theways described above, but a convenient method is for the interposinglayer or layers to consist of normal returns" without the addition ofany green ore.

In carrying out either or both of these last named processes we havefound that an inert layer of returns say from of an inch to about /2 aninch thickness acts very satisfactorily. The roasting actioninitiated atignition, and passing down through the charge passes satisfactorilythrough an interposed layer of limited thickness, the necessary heatbeing transmitted therethrough by air currents and by radiation andconduction. If for any reason, e. g. the desire to maintain higher gasstrengths ($02) or higher heat intensities or to use a thickerinterposed layer, it is undesirable to use an entirely inert material,then one or other of the means indicated above can be used to increasethe fuel value of the interposed layer.

The interposed layer can be inserted by means of any convenientmechanical arrangement. For example, a thickness of the normal charge toform the bottom layer can be fed on to the travelling grate in one orother of the well-known or recognized feeding devices, and then from asimilar and separate device the requisite thickness of the intermediatelayer (to form the parting layer) can be fed, followed by feeding on ofthe normal charge to form the top layer. In the case of using simplycoarser portions of the charge as the interposed layer to form theparting zone, this can be accomplished by carrying on' the firstoperation as above, and then passing to the third operation, butarrangingthe feeding on in such a manner as to allow the coarserparticles to roll down the feed heap, thus forming the coarser zone inbetween the other two.

The separate discharging of the layer or layers to be selected at ortowards the discharge end can be accomplished by any convenient device,as for example the edge of a metal blade or plate, or a row of prongs orforks on which the top layer, easily detached from the lower, rides overand reaching a conveyor is separately transported. The under portionofthe charge together with loose material takes the normal route of thesintering equipment, for example in the proces of British patentspecification No. 306,569 is used as returns. Alternatively, the upperportion can be returned or transported, and in general regarded as thenormal product, while the under portion at some convenient place in theequipment is diverted as the special output.

The position of the interposed layer within the cake can be chosen tosuit the quality requirements of the products, or the characteristics ofthe process. More than one layer can, if desired, be inserted e. g. twoinserted layers, giving three divisions of the charge.

Some practical examples will serve to illustrate various modes ofoperationz-taking the case of the process of British Patent No. 306,569,with certain zinc ores high in lead, say 4.5% Pb. In the normal processit will be found that the lead percentage in the sintered cake rangesfrom say 0.5% in the top to as high as 30% in the very bottom. By theuse of two inserted layers, it is thus possible to divide the outputinto three portions:the bottom portion high in lead and cadmium, whichcan be used for the recovery of lead and cadmium therefrom, the middleportion which can be used as normal output and/or for the supply ofreturns; the top portion low in lead and cadmium, which can be used forzinc distillation, or zinc oxide production, or other purposes. Anydeficiencies in the amount of returns required for the process can bemade up from one or other of the other portions, preferably the middleportion in normal modes of operation.

In the accompanying drawings there is illustrated a form of blastroasting apparatus designed for carrying on the process of the presentinvention; but it is to be understood that any other suitable form ofblast roasting apparatus may be employed in carrying on the saidprocess.

Referring to the accompanying drawings:-

Fig. 1 is a local view in side elevation of the upper portion of a blastroasting apparatus and showing diagrammatically the means for separatelyfeeding the respective 3 layers onto the endless travelling grate andthe means for effecting the separation of the top and bottom main layersafter roasting, and for removing said top layer and discharging thelatter (separately from the bottom layer) from the delivery end of thesintering machine;

Fig. 2 is a view in side elevationon a greatly enlarged scale-of: (a)one of the pallets pans or link members, forming the endless travellinggrate, in the tilted position which it is caused to assume on itsarrival at the discharge end of the endless travelling grate (as shownin Fig. 1) and (b) means for effecting the separation of the top andbottom main layers after roasting and for removing said top layer anddelivering the latter separately from the bottom layer, as each saidpallet in succession arrives at and passes under said means forseparating the top and bottom layers.

Fig. 3 is a fragmentary view, in plan, of Fig. 2;

Fig. 4 is a cross-sectional view on an enlarged scale on line l4 of Fig.1, of one of the pallets of the endless travelling grate. a

A is the endless travelling grate formed of pallets, pans or linkmembers a (hereinafter referred to as the pallets a) which are linked toone another, in any known or suitable manner to form the endlesstravelling grate of the blast roasting apparatus.

Each pallet a, on each side of itsupper surface, is provided with a sideflange a. '(Figf4), and is provided with flanged wheels I) which run onthe guide rails 33, B and D by which the 75 pallets are guided, exceptduring their travel along the longitudinal upper part of the roastingapparatus. During the travel ,of the pallets it along said upper 'partof the roasting apparatus, the bottom part of each pallet a. slidesalong the upper surface of the longitudinal member C on each side of theapparatus.

"Qio

At the discharge end of the apparatus the wheels b encounter and thenrun on the rail B which is curved downwards as indicated at B (seeFig. 1) After delivering the sintered material oil the palletsatthedischarge end of the apparatus the pallets ai'pass downwards around 1saidcurved end rail B their wheels 12 then engagingthe further rail Dwhich runs along the lower part of the apparatus.

c is the knife or plate having knife edgec of .the full width'of thelayers'of material carried travelling grate.

example hinged at c so on the endless travelling grate between theflanges a of the palletsja forming the'endless The knifje'or plate cisadjustably mounted, for that. the edge end -c or said 'knife or platecan be raised or lowered (and fixed in its adjusted position) to dividethe top layer of any desired thickness from the bottom layer on thegrate. d is shoot, down which the top layer divided byjthe knife orplate 0 is separately delivered,

for example to a conveyor (not,shown)..

e is roller, engaging on flange a on each side of the endless travellinggrate A.

r is shoot, down which is fed the desired mate-. I for initially formingthe. bottom layer 3, (see Fig. 2) of the desired rial or mixture 01'materials thickness, on' the pallets a of the endless travel- :linggrate A.

g is shoot, down which is i'ed-onto the top of the No."3 layer thedesired material for forming the intermediate layer 2; (ofthe desiredthick- I ness) to be interposed between the top layer l v and bottomlayer 3 --s ee Fig. 2.

h is shoot, down which is fed onto the top of the intermediate layer!the desired material or [mixture oi-materials forming the top layer I oithe desired thickness.

i t is the igniter.

v ,A simple mode of operationls'the insertion of only one interposed orparting layer, and with ores as above; assuming that the main aim 'isnot only, while sintering, (a) to cause the upper layer to becomerelatively free from lead or/and cadmium but also (b) to cause thesegregation-- of the lead or/and cadmium in. the bottom layer r 55 toenable the lead or/and cadmium 'tobe re-. covered from" said bottomlayer alter the latter has been separated, and delivered separately,

from the upper layer; thenthe interposedlayer would be inserted nearthebottom-oi the charge on the grate." In-this -oase. the top portioncan beutilized for'returns, as well as normaloutput;

while the separated bottom layeris selected and treated as aforesaid forlead or/and. cadmium recovery.- 7 L e5 v of.-a parting. layer nearthetop, and the selection 3 With ores lower in leadcontent,'theinsertion of the top layer as output gives agood low lead productwhichresults his good grade ot'metal (zinc! inthe zinc distillation processora good grade zinc oxide. g 4 When sintering zinc ores containins 'l.5%Pb, the uneven. lead distribution makes it possivble by theinsertion'oi' 'a .cleavage layer to obtain a topportionjassaying10.01%'1 b and lower.-

1 With the production of sintered material exilorming the'intermediatelayer as in either of travelling grate of a blast roasting apparatus andtravelling grate of a blastroasting apparatus and sintered on thetravellinggrate, which consists in delivering the charge tobe sinteredonto said high grade zinc oxides and/or high grade metallic zinc can beproduced therefrom.

,With' a negligible or very low lead and cadmium contentin the top layerwhen sintered, the 6 metal fromboth vertical and horizontal retortdistillation processes can be delivered substan: tially free from leadand cadmium.

-.Further, we. have found that with these low or negligible leadsinterstreated in the horizontal distillationprocess any small amounts of leadleft in the sinter come over in the earlier taps of the process, whilethe metal from the later taps is almost entirely free from lead andcadmium.

This is contrary to experience with/sinters or can be seen, therefore,that with these low lead sinters produced by the present invention, ahigh grade of zinc metal substantially free from both lead and cadmiumcan be obtained during the latter part of the distillation period.

It will be obvious that the present invention may be employed forre-sintering already sintered ore for the purpose of separatelyde-leading or de-cadmiumizing. such already sintered ore; namely by theaddition to and admixture with the already sinter'e'd ore of carbon (e.g. coal .or

. coke) in that part of the charge for forming the top and bottom layersof such sinter mixture and the/foregoing Examples (1, or b or 0; exceptthat in the case of Example cbeing employed a dif; ferent coke mixturewould be employed in the intermediate layer insteadoi' green ore.

. If desired the processor method of the present invention maybeemployed in the blast roasting" of any ore or ores (as well'as for zincsulphide ore) to which same maybe applicable. 7

What weclaim isz+ t 1. In the operation of sintering ore on the theremoval or substantial removal from the ore, during the sintering'operation, of lead and/or cadmium and/orother' impurities present in theore; the method of forming the charge. to be sintered on the travellinggrate which consists-in delivering onto said travelling grate the chargematerial in three superimposed :layers of diifer-' ing. characteristicsby interposing. between the top and bottom layers of the chargematerial, an 5n intermediate layer of charge material having (iii- 7ieringcharacteristics from the top and bottom layers andsuch that afterthe completion of. thesinterin'g operation this intermediate layer 'willconstituteja plane orzone of cleavage in the sintered charge thereby toenable the now substantially impurities-tree sintered top layer of the Tcharge to be-readily separatedfrom the bottom layer and to. beseparately delivered Irom the travelling grate; and separating said toplayer from thebottomlayer and delivering Qfromthe grate said toplayer'separately fromsaid bottom layer. z. l -2. Inthe operation of'sintering ore. on the the'removal or substantial removatiromdzheore,during the .sinteringioperation, of lead and/or; cadmium and/or otherimpurities present in the ore; the method of forming the charge to betravelling grate in more than three superimposed layers of material ofdifl'ering-characteristics in r such wise that an intermediate layer,i'ormed oi material of diflering characteristics from the v otherlayers, is interposed between the top layer and bottom layer and will,after completion of the sintering operation constitute a plane or zoneof cleavage in the slntered charge thereby to enable the nowsubstantially impurities-free slntered top layer to be readily separatedfrom the lower layers and to be separately delivered from the travellinggrate and separating said top layer from the lower layers and deliveringsaid top layer separately from said lower layers.

3. In the method of sintering ore according to claim 1, forming anintermediate layer between the top and bottom layers of a material whichremains inert throughout the sintering operation.

4. Inthe method of sintering ore according to claim 1, forming anintermediate layer between the top and bottom layers of a material ofcoarser grain size than that of the layer next above and below saidintermediate layer.

' 5. In the method of slntering ore according to claim 1, forming anintermediate layer between the top and bottom layers of a material offiner grain size than that of the layer next above and belowsaidintermediate layer.

6. In the method of sintering ore according to claim 1, forming anintermediate layer between the top and bottom layers oi! a material ofdifferent fuel value from that of the layer next above and below saidintermediate layer.

'7. In the method of sintering ore according to claim 1, forming anintermediate layer between the top and bottom layers of a material ofdifferent sulphur content from that of the layer next above and belowsaid intermediate layer.

STANLEY ROBSON. THOMAS BENSON GYLES.

